Dibromomethane (DBM) is an important solvent and chemical intermediate which is used in a large number of industrial applications. DBM is normally produced by the catalyzed halogen exchange of bromine for the chlorine contained in dichloromethane (DCM). One such process is described in German Patent No. 727,690. This process suffers from a number of drawbacks. The source of bromine is dry, gaseous HBr, which often contains considerable amounts of hydrogen, deriving from its manufacturing process. Hydrogen, being an inert gas in the DBM process, flows through the reactor, sweeping out part of the volatile DCM before it has time to react, thus decreasing the efficiency of the conversion. In addition, DCM is an expensive raw material, considering that 83% of its weight is wasted as HCl along with the excess HBr which is employed, making for an ecological problem. Disposal of spent catalyst is an additional ecological problem.
Other processes known in the art employ bromine salts instead of HBr. These processes, however, are inefficient and are not used in actual industrial applications. Thus, for example, NH.sub.4 Br in dimethylformamide (Neth. Appli. No. 6,607,498), and NaBr (U.S. Pat. No. 3,923,914) have been used for such purposes.
Direct bromination of methane at high temperatures has also been attempted, but resulted in low yields and reaction selectivity. Thus, for instance, German Patent No. 330,642 obtained a maximum of 44,4% DBM at 370.degree. C., in the presence of an iron catalyst.